Adds --add-file to allow adding files to initfs. (#302)

- Motivation is to be able to add the `swift-backtrace-static` binary as
needed.
- Use singlular `--add-file` and `--label` options since both accept
multiple invocations with single values each.

Example usage:

```bash
./bin/cctl rootfs create \
                --vminitd vminitd/bin/vminitd \
                --vmexec vminitd/bin/vmexec \
                --add-file /Users/john/.swiftpm/swift-sdks/swift-6.2-RELEASE_static-linux-0.0.1.artifactbundle/swift-6.2-RELEASE_static-linux-0.0.1/swift-linux-musl/musl-1.2.5.sdk/aarch64/usr/libexec/swift/linux-static/swift-backtrace-static:sbin/swift-backtrace \
                --label org.opencontainers.image.source=https://github.com/apple/containerization \
                --image vminit:latest \
                bin/init.rootfs.tar.gz
```

Makefile

@@ -62,8 +62,8 @@ init: containerization vminitd
 	@rm -f bin/init.rootfs.tar.gz bin/init.block
 	@./bin/cctl rootfs create \
 		--vminitd vminitd/bin/vminitd \
-		--labels org.opencontainers.image.source=https://github.com/apple/containerization \
 		--vmexec vminitd/bin/vmexec \
+		--label org.opencontainers.image.source=https://github.com/apple/containerization \
 		--image vminit:latest \
 		bin/init.rootfs.tar.gz
 

Sources/cctl/RootfsCommand.swift

@@ -34,23 +34,26 @@ extension Application {
         )
 
         struct Create: AsyncParsableCommand {
-            @Option(name: .long, help: "Path to vminitd")
-            var vminitd: String
+            @Option(name: [.short, .customLong("add-file")], help: "Additional file to add (format src-path:dst-path)")
+            var addFiles: [String] = []
 
-            @Option(name: .long, help: "Path to vmexec")
-            var vmexec: String
-
-            @Option(name: .long, help: "Platform of the built binaries being packaged into the block")
-            var platformString: String = Platform.current.description
-
-            @Option(name: .long, help: "Labels to add to the built image of the form <key1>=<value1>, [<key2>=<value2>,...]")
-            var labels: [String] = []
+            @Option(name: .customLong("ext4"), help: "The path to an ext4 image to create.")
+            var ext4File: String?
 
             @Option(name: .customLong("image"), help: "The name of the image to produce.")
             var imageName: String?
 
-            @Option(name: .customLong("ext4"), help: "The path to an ext4 image to create.")
-            var ext4File: String?
+            @Option(name: .customLong("label"), help: "Label to add to the image (format: key=value)")
+            var labels: [String] = []
+
+            @Option(name: .long, help: "Platform of the built binaries being packaged into the block")
+            var platformString: String = Platform.current.description
+
+            @Option(name: .long, help: "Path to vmexec")
+            var vmexec: String
+
+            @Option(name: .long, help: "Path to vminitd")
+            var vminitd: String
 
             // The path where the intermediate tar archive is created.
             @Argument var tarPath: String
@@ -90,18 +93,17 @@ extension Application {
 
             private func outputExt4(archive: URL, to path: URL) async throws {
                 let unpacker = EXT4Unpacker(blockSizeInBytes: 256.mib())
-
                 try unpacker.unpack(archive: archive, compression: .gzip, at: path)
             }
 
             private func outputImage(path: URL, reference: String) async throws {
                 let p = try Platform(from: platformString)
-                let labels = Application.parseKeyValuePairs(from: labels)
+                let parsedLabels = Application.parseKeyValuePairs(from: labels)
                 _ = try await InitImage.create(
                     reference: reference,
                     rootfs: path,
                     platform: p,
-                    labels: labels,
+                    labels: parsedLabels,
                     imageStore: Application.imageStore,
                     contentStore: Application.contentStore
                 )
@@ -142,6 +144,18 @@ extension Application {
                 entry.size = Int64(data.count)
                 try writer.writeEntry(entry: entry, data: data)
 
+                for addFile in addFiles {
+                    let paths = addFile.components(separatedBy: ":")
+                    guard paths.count == 2 else {
+                        throw ContainerizationError(.invalidArgument, message: "use src-path:dst-path for --add-file")
+                    }
+                    src = URL(fileURLWithPath: paths[0])
+                    data = try Data(contentsOf: src)
+                    entry.path = paths[1]
+                    entry.size = Int64(data.count)
+                    try writer.writeEntry(entry: entry, data: data)
+                }
+
                 entry.fileType = .symbolicLink
                 entry.path = "proc/self/exe"
                 entry.symlinkTarget = "sbin/vminitd"